Friendship is not the same as Affection, a stat introduced in Generation VI. However, in Let's Go, Pikachu! and Let's Go, Eevee!, the two appear to have been combined, since Affection does not exist in the game, but Pokémon with high friendship gain the same benefits as those that have high affection in other games.

In the core series games

Friendship debuted in Generation I as a mechanic that applied only to the player's Pikachu in Pokémon Yellow. In Generation II, it was expanded to cover all Pokémon. In all games, friendship is a value that ranges from 0 to 255 (stored as a single byte). In Pokémon Yellow, Pikachu's friendship is indicated by the expression it shows when the player talks to it, but in later games, certain NPCs in the games will evaluate the friendship of a Pokémon in the player's party.

A Pokémon's friendship is generally set when the player first obtains it. When a Pokémon is first caught from the wild, its friendship starts at its base friendship value. Trading a Pokémon also resets its friendship to its base value, unless it is being traded back to its original Trainer in Generation VI or later, in which case it regains the friendship it had before being traded away. A Pokémon caught in a Friend Ball starts with 200 friendship instead of its base friendship, while a Pokémon hatched from an Egg starts with 120 friendship.

Friendship is generally increased by taking good care of a Pokémon. Keeping a Pokémon in the player's party, raising it, using items on it, and getting it groomed will all increase a Pokémon's friendship. Letting it faint and using bitter herbal medicines on it will decrease a Pokémon's friendship.

Boosting friendship

In Pokémon Crystal, if a Pokémon is leveled up at its met location, it will gain twice as much friendship from that level up as usual. Since only Pokémon caught in Pokémon Crystal have a defined met location, Pokémon caught in the Generation I games, Pokémon Gold and Silver, and Pokémon from in-game trades will not receive this bonus. If a Pokémon that has a defined met location is traded to a Generation I game, this data is permanently erased, so it can no longer receive this bonus.

Starting in Generation III, if a Pokémon was caught in a Luxury Ball or is currently at the same location where it was caught (its met location), any increase to its friendship is boosted by an extra point (two points if both apply). If a Pokémon is holding a Soothe Bell, increases to its friendship are boosted by 50% of the change. In Generation III, Soothe Bell applies directly to the original change in friendship, while in later games, it applies to the the friendship change after including Luxury Ball and met location bonuses. In Generation IV, being at its met location does not change the amount of friendship a Pokémon gains, but it does from Generation V onward.

In Generation V, the Befriending Power Pass Power boosts any increase to friendship by one to three points depending on the strength of the power used. In Generation VI, the Befriending Power O-Power has the same effect. Befriending Power does not exist in Generation VII.

None of these effects change the amount of friendship lost for negative changes or for changes of 0 (such as using an X Attack on a Pokémon with high friendship).

Mechanics using friendship

In Pokémon Yellow, friendship affected very little beyond the reactions Pikachu would show when interacted with.

In Generation I

This section is incomplete.Please feel free to edit this section to add missing information and complete it. Reason: Double-check whether TMs/HMs can increase friendship even if they have no effect (like Potions and status-healing items).

Friendship in Pokémon Yellow affects very little. Outside of interacting with Pikachu, the only place where it has any effect is in determining whether Melanie will give the player a Bulbasaur in Cerulean City (which requires Pikachu's friendship to be at least 147).

In Pokémon Yellow, the player can check Pikachu's friendship by talking to it as it follows them in the overworld. A window will pop up showing Pikachu's face, and the expression reflects Pikachu's current friendship (though certain special events may elicit special reactions unrelated to Pikachu's current friendship). At maximum friendship, Pikachu will jump up and down before the window appears.

In the table below, the HP-restoring items and status condition healing items can increase Pikachu's friendship even if they have no effect. For example, attempting to use a Potion on Pikachu when it has full health will still increase its friendship.

In Generation II

In Generation II, friendship was expanded to cover all Pokémon. All Pokémon have a base friendship of 70, but any Pokémon caught in a Friend Ball starts with 200 friendship and any Pokémon hatched from an Egg starts with 120 friendship.

In Generation IV

This section is incomplete.Please feel free to edit this section to add missing information and complete it. Reason: Figure out the probabilities for the variable massage/grooming events.

The Pokétch's Friendship Checker app with a Drifblim at maximum friendship.

In Generation IV only, a Pokémon's met location does not affect the amount of friendship it gains. In Pokémon Diamond, Pearl, and Platinum, the massage at the Ribbon Syndicate is also not affected by any friendship boosts, and the Soothe Bell does not affect friendship gained when using a battle item.

In Generation VI

This section is incomplete.Please feel free to edit this section to add missing information and complete it. Reason: Check if Pokéblocks add friendship and chance of increasing friendship every 128 steps.

Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!

This section is incomplete.Please feel free to edit this section to add missing information and complete it. Reason: How to raise friendship (ie walking or feeding candy) and friendship benefits (ie those seen with affection).

In Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!, friendship is factored into all of a Pokémon's stats, except HP. At maximum friendship, a Pokémon will receive a 10% boost to its stats, before AVs are added in. The friendship multiplier scales directly with the level of friendship, starting from a 0% boost at 0 friendship to receiving the full 10% at 255.

FireRed and LeafGreen

"It couldn't possibly love you any more than it does now. Your Pokémon is happy beyond words."

255

"It looks very happy. I wish <rival> could see this and learn something from it."

200-254

"It's quite friendly with you. Keep being good to it!"

150-199

"It's warming up to you. Trust must be growing between you."

100-149

"It's not quite familiar with you yet. Pokémon are all quite wary when you first get them."

50-99

"<Player>, I don't like the way it glares at you. Could you try being a little nicer to it?"

1-49

"…Um, it's not easy for me to say this, but… Is there some reason why your Pokémon would hate you so much?"

0

XD: Gale of Darkness

The friendship rater is located inside the Krabby Club in Gateon Port. He is upstairs, straight to the rear of the club (not the ones backstage) and standing near the bartender. He looks like a boat captain. He is present after starting the events in Pyrite Town.

Statement

Friendship

"It simply adores you! It couldn't possibly get to like you more. This is wonderful!"

255

"It seems to like you very much. Your Pokémon seems to be very happy that it's with you."

200-254

"It likes you quite a bit. It wants to be pampered by you."

150-199

"It's growing friendly toward you. It seems to believe in you."

100-149

"It doesn't seem to be used to you yet. You should treat it kindly."

50-99

"Hmm… It's not friendly toward you. The look in its eyes is frightening. You should treat it more kindly."

1-49

"… This is awful. It detests you to a degree I hardly ever see. Are you sure you'll be okay?"

Pokémon Ranger: Shadows of Almia

Friendship also has an effect in the second game of the Pokémon Ranger series. Partner Pokémon can have the condition of Fine, Happy, or Very Happy. When it is in a Happy Mood, black musical notes appear to come out of it. Multicolored musical notes come out when it is Very Happy. This may happen whether or not it is with the player. This state of mind increases the speed the Partner Gauge fills up due to more Partner Energy being provided.

Pokémon that have friendly relationships with their Trainers are said to perform better in battles. Ash believes that befriending a Pokémon will make it grow stronger, and he treats all his Pokémon with utmost care and respect. However, over the course of the series, some Trainers have been shown to focus on raw strength alone, disregarding their Pokémon's feelings and well being. Examples include Paul and Cross.

In Our Cup Runneth Over!, Contest Master Wallace stressed out the importance of kinship. He also said that playing with Pokémon can help Trainers and Coordinators in learning how to bring out the potential of their Pokémon. In addition to enhancing a Pokémon's appearance, Pokémon grooming is said to make them happier. Trainers who devote themselves to the development of techniques that improve a Pokémon's health and happiness are known as Pokémon Breeders. There are also people who study to become Pokémon Connoisseurs in order to be able to identify the compatibility between Trainers and Pokémon, and then offer advice on how to strengthen their friendship.

In contrast with the games, where a Pokémon of a certain level will only obey its Trainer if he or she possesses specific achievements, disobedient Pokémon in the anime will gain respect for their Trainers after realizing how far the Trainer is willing to go to befriend, protect, and care for the Pokémon.